Method of recovering materials bound to a metallic substrate using cryogenic cooling

ABSTRACT

A recycling process that facilitates separation of materials from metallic substrates by cryogenically cooling the recyclable items to induce embrittlement of the metals. Embrittled metals may be shattered more efficiently and with a higher yield of materials bound to the metallic substrates. Metal embrittlement may be induced by mixing the source stream with liquid nitrogen, and cooling the stream to approximately minus 200° F. Multiple recovery stages may be employed to maximize the yield of the target materials. Embodiments may enable recovery of platinum group metals (PGMs) from catalytic converters with metallic foil substrates. Yield of PGMs may be enhanced by employing a primary recovery stage and a secondary recovery stage, by cryogenically cooling input materials for each stage, by mixing the pulverized material in secondary recovery with an aqueous solution to dissipate attractive charges, and by wet screening the pulverized material slurry to obtain the PGM particles.

BACKGROUND OF THE INVENTION Field of the Invention

One or more embodiments of the invention are related to the field ofmetal recycling. More particularly, but not by way of limitation, one ormore embodiments of the invention enable a method of recoveringmaterials bound to a metallic substrate using cryogenic cooling.

Description of the Related Art

Recycling of industrial or consumer products generally involvesseparating the recyclable items into their constituent materials.Materials bound to a metallic substrate are often difficult to recovereconomically. A particular challenge is recovery of platinum groupmetals (“PGMs”) from catalytic converters. Because PGMs are extremelyexpensive, recovering a large fraction of the PGMs from a recycledcatalytic converter is highly valuable.

Existing processes to recover PGMs from catalytic converters withmetallic foil substrates generally recover only about 80% to 90% of thePGMs bound to the metallic substrate. The remaining unrecovered PGMs arelost as waste when the fragments of the metallic substrate are recycledas scrap metal. For example, existing processes may leave approximately5 ounces of unrecovered palladium per ton of metallic substrate.Although this amount is tiny as a percentage of material, the high priceof palladium (currently approximately $1,100 per oz.) implies that$5,500 of palladium is discarded per ton of recycled substrate. Existingprocesses are not able to capture this value.

Existing PGM recovery processes generally use very powerful equipment tomechanically crush and grind metallic substrates into small particles.This equipment increases the cost of recovery operations due to highenergy use, high capital costs, and high equipment maintenance costs.

Some existing PGM recovery processes also generate environmentally toxiciron oxide metal sludges as waste. These sludges typically go intolandfills, which creates a potential liability for the recycler due toenvironmental contamination. The recycler also may have to pay todispose of the waste, which further increases the cost of the recyclingoperation.

These three issues with existing recovery processes—incomplete recovery,expensive heavy-duty equipment, and environmentally toxic waste—may beaddressed with a recovery process that uses cryogenic cooling. Metalscan be cryogenically cooled to very low temperatures inexpensively, forexample using liquid nitrogen. In recycling, cryogenically cooled metalscan be shattered more efficiently and effectively, using lower powerequipment. In addition, use of cryogenic cooling increases the yield ofPGMs from metallic substrates. Yields can be further enhanced by usingtwo separate recovery stages, and by performing separation in waterrather than in air. Cryogenic cooling, two-stage recovery, and waterseparation have not been applied in recovery of materials from metallicsubstrates. A recovery process that uses cryogenic cooling is also aclean process that does not generate toxic waste, since both PGMs andmetallic substrates can be recycled.

For at least the limitations described above there is a need for amethod of recovering materials bound to a metallic substrate usingcryogenic cooling.

BRIEF SUMMARY OF THE INVENTION

One or more embodiments described in the specification are related to amethod of recovering materials bound to a metallic substrate usingcryogenic cooling. Embodiments of the invention may cool recyclableitems to a low temperature to induce embrittlement of metals, therebyincreasing recovery efficiency and yield.

One or more embodiments of the invention may enable recovery of one ormore target materials bound to a metallic substrate using the followingsteps: obtaining a source stream of recyclable items, cryogenicallycooling the stream, applying mechanical forces to break apart themetallic substrate into pieces, forming a mixture stream containingpieces of the substrate and all or a portion of the target materials,and feeding the mixture stream into a separator to separate the targetmaterials from the substrate pieces. The recyclable items in the sourcestream may each have a metallic substrate to which one or more targetmaterials are coupled. The cryogenic cooling reduces the temperature ofthe stream to a point that induces embrittlement of the metallicsubstrates. Mechanical forces applied to the embrittled substratesbreaks these substrates into pieces, and releases all or a portion ofthe target materials. The separator generates one or more firstfractions that contain the substrate pieces, and one or more secondfractions that contain target materials. In one or more embodiments theseparator may have one or more screen meshes that separate pieces orparticles by size.

In one or more embodiments of the invention, each recyclable itemcontains all or a portion of a metal foil catalytic converter substrate,and the target materials are one or more platinum group metals, such asplatinum, palladium, and rhodium.

In one or more embodiments, cryogenic cooling may be performed by mixingthe source stream with liquid nitrogen. The resulting cooled stream maybe cooled to a temperature at or below minus 150 degrees Fahrenheit. Inone or more embodiments the cooled stream may be cooled to a temperatureat or below minus 200 degrees Fahrenheit. In one or more embodiments thecooled stream may be cooled to a temperature at or below minus 250degrees Fahrenheit.

Cryogenic cooling of the stream may be performed to induce embrittlementof the metallic substrate and of the target materials. Depending on thematerials in the substrate and on the target materials, differenttemperatures may be desirable to induce embrittlement. For example, ifthe substrate or the target materials include iron or an iron alloy, thecooled stream may be cooled to a temperature at or below minus 150degrees Fahrenheit. If the if the substrate or the target materialsinclude palladium or rhodium, the cooled stream may be cooled to atemperature at or below minus 200 degrees Fahrenheit. If the substrateor the target materials include platinum, the cooled stream may becooled to a temperature at or below minus 250 degrees Fahrenheit.

In one or more embodiments, the metallic substrate of the recyclableitems may contain a FeCrAl alloy. Cryogenic cooling of the recyclableitems may include mixing the source stream with liquid nitrogen in aratio of at least one liter of liquid nitrogen to each one kilogram ofFeCrAl alloy, and cooling the source stream to a temperature at or belowminus 200 degrees Fahrenheit.

In one or more embodiments, each recyclable item may be a fragment froma metal foil catalytic converter substrate that is generated by aprimary recovery process that recovers a portion of the targetmaterials. The fragments may contain an additional quantity of targetmaterials that this primary recovery process did not recover. One ormore embodiments of the invention may enable recovery of some or all ofthis additional quantity of target materials. This process may bereferred to as “secondary recovery,” for example. One or moreembodiments of the invention may encompass either or both of primaryrecovery and secondary recovery.

In one or more embodiments that perform secondary recovery, applyingmechanical forces to break apart the cooled stream may includeshattering the fragments using an impact mill. The impact mill may beconstructed of mill materials that do not shatter or break at thetemperature of the cooled stream; these mill materials may includestainless steel containing nickel, for example.

In one or more embodiments that perform secondary recovery, forming amixture stream after applying mechanical forces to the cooled stream offragments may include screening the pieces generated by the mechanicalforces to obtain particles that pass through an output screen, and thenmixing the stream of particles with a liquid. The liquid may contain anelectrolyte and a surfactant. The output screen may for example be ofmesh size in a range of 6 mesh to 10 mesh. (Mesh size of a screen is thenumber of openings in the screen per linear inch of screen; thus alarger mesh size corresponds to a finer mesh.) The mixture stream ofparticles plus liquid may be fed into an electrically grounded unit thatagitates the stream and dissipates electrical charge on the particles.On exiting this electrically grounded unit, the stream may be fed to aseparator with a screen mesh of mesh size in a range of 100 mesh to 150mesh. The fraction of particles and liquid that passes through thisscreen mesh may then be processed to remove moisture, leaving the targetmaterials (such as platinum group metals). For example, the fraction maybe fed into a settling tank, and the particles may be allowed to settleto the bottom of the tank. Liquid may then be evacuated from the top ofthe tank, leaving a filter cake that may then be further dried withheat.

One or more embodiments of the invention may perform or include primaryseparation, where the source stream contains metal foil catalyticconverter substrates. The source stream may be cryogenically cooled, andthen mechanically reduced by crushing the outer can casing of thecatalytic converters, and shredding the crushed catalytic converters torelease a portion of the target materials. The shredded material may befed to a separator with a top screen and a bottom screen with a finermesh than the top screen. The separator generates three fractions: alarge pieces fraction that does not pass through the top screen, a smallpieces fraction that passes through the top screen but not through thebottom screen, and a particles fraction that passes through bothscreens. The top screen may have for example a ¼ inch mesh size, and thebottom screen may have for example a size 10 mesh. The particlesfraction contains a portion of the target materials. The large piecesfraction may be reintroduced into the shredding operation. The smallpieces fraction may be input into a secondary recovery process torecover more of the target materials that remain bound to the smallpieces.

One or more embodiments of the invention may encompass both primaryrecovery and secondary recovery. The source stream for primary recoverymay be catalytic converters with metallic substrates. Primary recoverymay recover a portion of the PGMs from the metallic substrates, and maygenerate pieces of the substrates that are transmitted to secondaryrecovery. Secondary recovery may further process these pieces to recoveran additional quantity of the PGMs.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the inventionwill be more apparent from the following more particular descriptionthereof, presented in conjunction with the following drawings wherein:

FIG. 1 shows an illustrative recycling requirement that may be addressedby one or more embodiments of the invention: recycling of metal foilcatalytic converters to recover precious metals such as platinum,palladium, and rhodium bound to the metal foil substrate.

FIG. 2 shows a typical process used in the art to recover platinum-groupmetals from catalytic converters using high energy crushing or grindingat ambient temperature.

FIG. 3 shows an overview of a recovery process enabled by one or moreembodiments of the invention. This illustrative process uses a primaryrecovery stage followed by a secondary recovery stage; each stage beginsby cryogenically cooling materials to embrittle metals to facilitatemechanical reduction and separation.

FIG. 4 shows an illustrative cryogenic cooling process that may be usedin primary or secondary recovery in one or more embodiments.

FIG. 5 shows a flowchart of an illustrative primary recovery processthat may be used in one or more embodiments.

FIG. 6 shows a flowchart of an illustrative secondary recovery processthat may be used in one or more embodiments.

FIGS. 7 and 8 show side and top views, respectively, of a customizedcarousel that may be used in one or more embodiments of the invention toreceive and cryogenically cool recyclable material, and then to feed thecooled material to a crushing unit.

DETAILED DESCRIPTION OF THE INVENTION

A method of recovering materials bound to a metallic substrate usingcryogenic cooling will now be described. In the following exemplarydescription, numerous specific details are set forth in order to providea more thorough understanding of embodiments of the invention. It willbe apparent, however, to an artisan of ordinary skill that the presentinvention may be practiced without incorporating all aspects of thespecific details described herein. In other instances, specificfeatures, quantities, or measurements well known to those of ordinaryskill in the art have not been described in detail so as not to obscurethe invention. Readers should note that although examples of theinvention are set forth herein, the claims, and the full scope of anyequivalents, are what define the metes and bounds of the invention.

FIG. 1 shows an illustrative application of a recovery process enabledby one or more embodiments of the invention: recovery of platinum-groupmetals (“PGMs”), such as platinum, palladium, and rhodium, fromcatalytic converters with metal foil substrates. A catalytic converter101 may contain a metal-foil substrate 102 that provides a large numberof channels through which exhaust gas passes. The channels of thesubstrate 102 may for example be made of a FeCrAl alloy 103, or anothermetal or mixture of metals. A washcoat is generally bonded to thesubstrate surface; the washcoat material 104 may for example contain analuminum oxide base into which platinum-group metals are added. The PGMsact as catalysts for the conversion of exhaust gasses to other lesstoxic substances. PGMs used in catalytic converters may include forexample, without limitation, any or all of platinum, palladium, orrhodium. Other materials may be used as catalysts instead of or inaddition to these three elements.

Because the PGMs in catalytic converter washcoats are extremelyvaluable, a recycling process 105 may be used to recover a portion ofthese metals from the metallic substrate with the bonded washcoatcontaining the PGMs. The products of the recovery process may includethe PGMs 106 and potentially the metal alloy 107 from the substrate.

The application of PGM recovery from catalytic converters is anillustrative application of one or more embodiments of the invention.One or more embodiments may be used to recover any material or materialsbonded to a metallic substrate. The metallic substrate may be anystructure, item, scaffolding, frame, container, part, or assembly ontowhich or into which one or more other materials are attached, mixed, orotherwise coupled. Bonding of materials to the substrate may be via anychemical or physical processes. Recovery of the materials may beperformed for example as part of recycling of a product or structurecontaining the metallic substrate. Illustrative applications ofembodiments of the invention in addition to PGM recovery from catalyticconverters may include for example recycling of automotive air fuelratio sensors, recycling of pre-catalytic converters, and recycling ofO2 oxygen sensors post catalytic conversion. These illustrativeapplications also require separation of target materials from metallicsubstrates, and may be performed more effectively and efficiently usingcryogenic cooling of materials.

FIG. 2 shows an illustrative process known in the art for recovery ofPGMs from a catalytic converter metal foil substrate. A batch 201 ofcatalytic converters to be recycled is the input into the process. Theknown process may for example use mechanical forces to mechanicallyreduce the substrate of the catalytic converters 201 to small pieces,and to separate the washcoat from these pieces using high mechanicalforces. For example, a crush step 202 may break the substrate intofragments, and a subsequent grind step 203 may further reduce the sizeof these fragments. A separation step 204, such as a screeningoperation, may filter out the remaining metallic fragments from theliberated washcoat materials. The fractions from step 204 may thereforeinclude a fraction containing the PGMs 106, and a fraction 210containing metallic fragments. These fragments 210 may for example bewaste or they may be recycled as scrap metal 211.

While the process illustrated in FIG. 2 does recover some of the PGMs inthe catalytic converters 201, the recovery is incomplete because thesubstrate fragments 210 still contain a significant amount of PGMs inwashcoat that remains attached to the fragments. Because of the highprice and scarcity of PGMs, it is attractive to recover all residualPGMs in the fragments 210; however, existing processes known in the artsimply recycle the fragments as scrap metal rather than performingadditional recovery operations to obtain the remaining PGMs. Inaddition, the recovery operations 202 and 203 are energy intensivebecause very high-power machines are required to crush, grind, orotherwise mechanically reduce the catalytic converters 201 and toliberate a portion of the PGMs 106. And finally, the separation step 204is typically performed in air (for example with a vibratory screen),which limits the extent to which PGMs can be separated from thefragments to which they are bonded.

One or more embodiments of the invention may improve the yield andefficiency of recycling operations to recover PGMs or other materialsbound to a metallic substrate, such as the substrate of a catalyticconverter. FIG. 3 shows an overview flowchart of one or more embodimentsof the invention that provide these improvements. The recovery processillustrated in FIG. 3 includes a primary recovery stage 301 a and asecondary recovery stage 301 b. The primary recovery stage 301 a obtainsa source stream 201 of recyclable items, such as catalytic converters orparts thereof. It generates recovered materials 106 a, and pieces,fragments, or other byproducts 210 a that may contain additionalquantities of the target materials (such as PGMs) that have not beenrecovered in the primary recovery. The stream 210 a is then input into asecondary recovery stage 301 b. Secondary recovery recovers additionalquantities of the target materials 106 b, and residual metal fragmentsor particles 310 that may be input to a metal recovery process 311.

One or more embodiments of the invention may include primary recoveryonly, secondary recovery only, or both primary and secondary recovery.One or more embodiments may include more than two stages of recovery, orany number of stages. In one or more embodiments, secondary recovery maybe performed on materials obtained from one or more other primaryrecovery processes 320, instead of or in addition to materials outputfrom a primary recovery process 301 a enabled by the embodiment. Forexample, without limitation, the source stream 210 a for secondaryrecovery stage 301 b may be obtained from or mixed with an output 210from the existing process shown in FIG. 2.

In the embodiment illustrated in FIG. 3, the major types of steps inprimary recovery 301 a and secondary recovery 301 b are similar: eachincludes a cryogenic cooling step, followed by a mechanical reductionstep, and then followed by a separation step. The detailed operationswithin these steps may differ considerably between primary and secondaryseparation, as described below for example. Moreover, additional stepsmay be present in one or more embodiments in either or both of primaryand secondary recovery. Source stream 201 contains recyclable items withone or more target materials bound to a metallic substrate. This sourcestream is input into a cryogenic cooling step 302 a that cools thesource stream items to a low temperature where the metals in the itemsbecome embrittled. The cooled stream 303 a with embrittled metals isthen input into one or more mechanical reduction steps 304 a, which usemechanical forces to break apart the metallic substrate into pieces.Because the metals are embrittled, the forces and power required tobreak apart the substrate are considerably lower than those of typicalmechanical reductions such as the steps 202 and 203 illustrated in FIG.2. The mechanical reduction step or steps 304 a may also liberate aportion of the target materials (such as PGMs) from the substrate. Thepieces of the mechanical substrate and the liberated target materialsare combined into a mixture stream 305 a, with other materialspotentially added as well into this mixture, and this stream 305 a isinput into a separation step 306 a. The separation step 306 a, which mayfor example screen or sort particles by size or other properties intodifferent fractions, generates recovered target materials 106 a, andremaining substrate pieces 210 a. Secondary recovery 301 b may proceedto recover additional target materials from the substrate pieces 210 a.The major steps of secondary recovery may be similar to those of primaryrecovery: cryogenic cooling 302 b to form a cooled stream 303 b withembrittled metals, followed by application of mechanical forces 304 b tobreak the pieces into smaller particles and liberate additional targetmaterials, followed by formation of a mixture stream 305 b that isseparated in step 306 b into target materials fraction 106 b and metalparticles 310. As described in detail below, separation step 306 b maybe performed in an aqueous solution, rather than in air, which mayincrease the effectiveness of this step.

Cryogenic cooling in primary or secondary recovery may be performed toinduce embrittlement of the metals in the source streams. In recovery ofPGMs from catalytic converters, this cooling may for example rearrangethe atomic structure of metal foil catalytic converter substrates (whichmay be for example FeCrAl alloys), thereby causing metal embrittlement.Pretreating the source streams to embrittle the metals may producematerials that are suitable for introduction into mechanical reductionoperations, such as crushing, grinding, pulverizing, and shredding. Theembrittled metals may be easier to break into pieces with lower-power,lighter duty equipment, making the mechanical reduction steps moreenergy efficient. Lower-power, lighter duty equipment may also requireless capital and less expenditure for maintenance.

FIG. 4 shows an illustrative cryogenic cooling process that may be usedin one or more embodiments. Liquid nitrogen 401 may be added to sourcestream 201 or 210 a (or both), for example by spraying liquid nitrogenonto the materials or flooding a container of materials with liquidnitrogen. Embrittlement occurs in ferritic steel alloys at extremely lowtemperatures—typically at minus 150 degrees Fahrenheit. Embrittlementtemperatures for PGMs are not readily known in the art; however, theinventor has determined experimentally that palladium and rhodium areembrittled at approximately minus 200 degrees Fahrenheit, and platinumis embrittled at approximately minus 250 degrees Fahrenheit. Becauseliquid nitrogen has a temperature of approximately minus 320 degreesFahrenheit, exposure to a sufficient quantity of liquid nitrogen for asufficient time can successfully embrittle almost all metals ofinterest, either substrate materials or target metal materials.Illustrative exposure parameters that may be used in one or moreembodiments may be for example use of a quantity of liquid nitrogen in aratio 402 of one liter of liquid nitrogen for every one kilogram ofFeCrAl in the source stream, and exposing the source material to thisquantity for a time 403 of approximately 6 minutes. These parameters mayresult in cooling the source materials to temperature 404 of minus 200to minus 250 degrees Fahrenheit (depending on the PGMs present in thecatalytic converters), which induces embrittlement 405 of both FeCrAland PGMs. These parameters are illustrative; one or more embodiments mayuse different amounts and exposure times, for example for differenttypes of source streams, metallic substrates, and target materials. Inone or more embodiments, more than one liter of liquid nitrogen perkilogram of FeCrAl may be used, for example to cool the stream faster.Use of liquid nitrogen as a cryogenic cooling solution is alsoillustrative; one or more embodiments may use any type of cooling toinduce embrittlement of one or more metals in the source stream orstreams.

FIGS. 5 and 6 show illustrative operations that may be used in one ormore embodiments to perform the steps of primary and secondary recovery,respectively. The example processes and operations shown in thesefigures illustrate recovery of PGMs from catalytic converter metallicfoil substrates; similar processes may be used in one or moreembodiments for recovery of other target materials from other metallicsubstrates.

In the primary recovery stage shown in FIG. 5, source stream 201contains catalytic converters or portions thereof. This stream is inputinto cryogenic cooling operation 501, which uses liquid nitrogen asdescribed in FIG. 4 to generate a cooled stream of material 502 atapproximately minus 200 degrees to minus 250 degrees Fahrenheit. Thiscooling operation may be performed for example by loading a batch ofmetal foil catalytic converter substrates into a vessel compartment.Liquid nitrogen may be flooded into the vessel, filling the vesselsufficiently to cover the top layer of material. Initially the materialwill vigorously react to the cooling process. After exposure forapproximately 6 minutes, the material will be sufficiently cooled andthe metals embrittled. FIGS. 7 and 8 below show equipment that may beused for this cooling operation in one or more embodiments.

Batches of the cooled stream 502 (such as a batch in a vessel container)may then be discharged into a jaw crusher for crushing operation 503.The purpose of this operation is to shatter the outer can casingfraction of the metal foil catalytic converter substrates material,reducing the screen size and thereby liberating dissimilar materials anddelivering stress relief for downstream shredding operations. Jawcrushers vary from laboratory sized through large rock crushing units.Most are simply not suited for this operation. An illustrative unit thatis effective for this operation is a Lippmann Engineering model #490306with 15″×24″ manganese jaws fitted with a 30 hp electric motor. Thecryogenically treated metal foil catalytic converter substrates (FeCrAlalloys) may be gravity fed into the jaw crusher. The crusher may be setto shatter the outer can casing with an approximate 1″ jaw setting.Efficient crushing or shattering requires the use of “choke feeding” ofthe jaw crusher and must be strictly observed, hence the need for basketbatch feeding. The crushed material 504, with the outer can shattered,may be discharged into a hopper located beneath the crusher and sent tothe shredding operation 505 for further mechanical reduction.

The purpose of shredding operation 505 is to reduce the size of thecrushed material 504, and to liberate the majority of platinum groupmetals and ceramic of the crushed metal foil catalytic convertersubstrates. Crushed material may be reduced for example to particles ofsize ¼″ or smaller. These particles may then be fed into a secondaryrecovery process, as described below with respect to FIG. 6. Metal foilcatalytic converter substrates (FeCrAl alloys) will exit the jaw crusherand enter the rasper. The rasper may for example have a singlehigh-speed rotor with many specially hardened grinding teeth. Thematerial will be forced between the rotor and fixed anvil. This resultsin a high liberation of the coating of ceramic and precious metals fromthe FeCrAl alloy substrate. An illustrative rasper that may be used forshredding is a 75 HP rasper single rotor fitted with a ¼″ output screen.Illustrative manufacturers that provide suitable raspers include forexample SSI and Komar.

The output of the shredding operation 505 is a mixture 506 containingpieces of shredded substrate and liberated PGMs and ceramic materialfrom the washcoat. This mixture 506 is input into a vibratory screeningoperation 507 to separate the PGMs and ceramic fraction from the FeCrAlsubstrate. An illustrative screening operation may for example use avibratory screen fitted with a top ¼″ screen, and a bottom screen ofsize 10 mesh. An illustrative manufacturer of an appropriate vibratoryscreen is Sweco. The vibratory screen may be fitted with a top toeliminate dust from the screening operation. This screening operationwill produce three fractions. The first fraction 508 is pieces andparticles of size greater than ¼″. This fraction may be reintroducedinto the rasper shredding operation 505. The second fraction 509 isparticles of size between ¼″ and 10 mesh. These particles may forexample be fed to secondary recovery stage 301 b to recover additionalPGMs. The third fraction 510 is particles of size less than 10 mesh.This fraction contains an extremely high concentration of the preciousmetals 106 recovered and is suitable for shipment to a precious metalsmelter.

FIG. 6 shows illustrative operations that may be used in secondaryrecovery in one or more embodiments. Source stream 210 a for secondaryrecovery may for example contain the fraction 509 from primary recoveryas illustrated in FIG. 5. It may also or alternatively contain materialfrom a different primary recovery process. The source stream may be fedfor example into a bulk hopper feeder 601. When coupled to a primaryrecovery process such as the process shown in FIG. 5, the hopper 601 mayact as a surge bin for receiving shredded metal fragments from thevibratory screen output second fraction 509. Shredded metal foilcatalytic converter substrates (FeCrAl alloys) flows from the vibratoryscreen into the hopper. The hopper 601 acts as interim storage of thematerial as it flows out its bottom discharge outlet conveyed by thevibrating feeder into the cryogenic auger described below. A suitablehopper is for example a large bulk hopper with enough cubic feet ofcapacity, fitted with appropriate Syntron or equivalent type vibratorydischarge feeder.

Output from the hopper 601 is input into cryogenic cooling operation602. As described above with respect to primary recovery, the purpose ofcryogenic cooling is to induce metal embrittlement. This may be achievedby mixing liquid nitrogen with the material in a ratio of one liter ofnitrogen to each one kilogram of FeCrAl. An illustrative cryogeniccooling operation may for example use a cryogenic screw conveyormanufactured out of stainless steel. The conveyor unit may for examplebe PLC controlled with three cooling zones, allowing for precise controlof the material feed and the liquid nitrogen input. The shredded metalfoil catalytic converter substrates (FeCrAl alloys) exit the bulk feederhopper 601 into this cryogenic screw conveyor. As the material movesthrough the tunnel, liquid nitrogen is sprayed onto the FeCrAl metalfoil substrates. At the time FeCrAl metal foil substrates exit thecryogenic screw conveyor, optimum metal embrittlement temperature hasbeen achieved in cooled stream 603. The screw conveyor turnssufficiently slowly (for example, at 5 RPM) to allow the metal to coolto the desired temperature.

Cooled stream 603 is then input into pulverizing operation 604. Thisoperation reduces the feed particles (which may be up to ¼″ in size) tobelow 6 mesh. An illustrative impact mill that may be used forpulverizing is a 30 HP Fitzmill pulverizer hammer mill. All contactparts of the mill must be made of materials that do not shatter at thenegative 200 to negative 250 degrees Fahrenheit temperature of thecooled stream 603. For example, they may be made of stainless-steelconstruction containing nickel for safe cryogenic grinding operations.The mill may be operated for example at 3,600 rpm, and may be fittedwith a 6 mesh output screen. In one or more embodiments a finer meshoutput screen may be used, for example an output screen in the range of6 mesh to 10 mesh. A finer output mesh may reduce particle sizes fordownstream operations, which may improve downstream efficiency; however,it may also reduce throughput from the pulverizing operation. Differentembodiments of the process may therefore use different mesh sizes tooptimize various aspects of the process.

The cooled stream 603 of ¼″ or below metal foil catalytic convertersubstrates (FeCrAl alloys) at embrittlement temperature may becontinuously feed into the impact mill. Shattering occurs in this stepfollowed by attrition grinding. Shattering will liberate the ceramiccoated with precious metals during the introduction of embrittled lowtemperature feed stock traveling at slow speed then encounteringultra-high-speed hammers. The energy transmission at the point ofcontact will produce the desired shattering effect. This coupled withadditional attrition grinding will cause any platinum or palladium metalalloyed on the surface with the FeCrAl alloy (diffusion bonding ofplatinum metals) to liberate (sand blasting affect) and become free.Static electricity produced by the high-speed rotor will cause all thedissimilar particles to obtain a positive electrical charge and becomeattracted hence coating one another. This static electrical charge mustbe dissipated in the downstream equipment to optimize recovery ofprecious metals.

The output 605 from the impact mill contains particles of size below 6mesh. These particles are then mixed in step 606 with an aqueoussolution to form a mixture stream 607. This mixing may occur for examplein a water injection plenum. An illustrative plenum may be for example astainless-steel plenum that may be mounted directly underneath andattached to the pulverizer, with two opposing water injector spraynozzles. As the pulverized mixed metal stream exits the pulverizerscreen and enters the water injection plenum it encounters the waterinjector spray nozzles. The desired effect is to produce a slurry andcoat all particles with process water that has been conditioned. Thewater may for example be a solution containing an electrolyte and asurfactant. This conditioned process water acts as a wetting agent aswell as an electrolyte. The surfactant reduces surface tension, allowingfor better mixing of the particles in the aqueous solution. Mixing theparticles with process water also prevents the formation of dust, whichwould otherwise cause loss of some of the PGM particles.

The slurry 607 then flows to a trommel unit for a wash operation 608.This operation has two purposes: First it dissipates the staticelectrical charge all particles have acquired in the pulverizer. Secondit acts as a washing unit to scrub particles clean to free alldissimilar particles from each another. This scrubbing is more effectiveat separating particles than an air separation with a vibratory screen.An illustrative trommel that may be used in one or more embodiments is a5 hp trommel fitted with lift bars and an exit screen for material tofreely exit the machine. The unit should be adequately grounded toearth. The trommel unit may rotate at approximately 25 RPM. As theslurry travels through the trommel it encounters lift bars that createturbulence and contact with the metal parts of the trommel. Theconditioned water provides the necessary conductivity for the staticelectrical charge to run to ground through the unit, thereby freeing allparticles from attraction to each other. The washed and grounded slurryexits and flows to a wet screening operation.

Wet screening performs final separation of the slurry into a fractioncontaining PGMs and ceramic and a fraction containing the FeCrAlsubstrate. The illustrative wet screening process shown in FIG. 6performs two stages 609 a and 609 b of rinsing and screening. One ormore embodiments may use any number of wet screening stages. Eachscreening stage may use a vibratory screen, for example a screenmanufactured by Sweco. The two vibratory screens used in wet rinse andscreen operations 609 a and 609 b may for example each be fitted with asingle 150 mesh wire cloth screen. Each screening operation produces twofractions. The first fraction produced is 150 mesh plus FeCrAl metalreject. The second fraction is the precious metal water slurry. As thetrommel unit discharges the mixed metal slurries onto the firstvibratory screen, rinse water is applied at varies points across thescreen rinsing the metal slurry. The liberated precious metal fraction611 a of the slurry is 300-600 mesh and it classifies and separates fromthe FeCrAl metal. The rinsed FeCrAl metal 610 a is discharged from thefirst vibratory screen and enters the second vibratory screen for afinal rinse phase 609 b. The rinse water 611 a from the first stage 609a is combined with rinse water 611 b from the second stage to form rinsewater 612; this rinse water 612 contains the PGMs. The rinse waterstream 612 is pumped to a settling tank. The rinsed FeCrAl metal 310discharges into a bulk bag (super sack) for collection. This metal 310may for example shipped to a steel processor for melting and fabricationinto new ferritic alloy products.

In one or more embodiments of the invention, the screening operations609 a and 609 b may use output screens with a mesh size below 150 mesh,for example a mesh size between 100 mesh and 150 mesh. The optimal meshsize may depend for example on the output screen size from thepulverizing operation 604. For example, with a 6 mesh output screen forpulverizing, the wet screening operations 609 a and 609 b may usescreens of size 100 mesh; with a 10 mesh output screen for pulverizing,the wet screening operations 609 a and 609 b may use screens of size 150mesh. These mesh size values are illustrative; one or more embodimentsmay use any desired mesh sizes for any of the steps in the process.

The PGM-bearing slurry 612 is input to operation 613 to remove the PGMsfrom the rinse water. One or more settling tanks receive the slurry.Settling tanks may be for example cone shaped bottom discharge polytanks of adequate storage capacity to accommodate the desired productflows. An empty tank accepts PGM-bearing slurry process water from wetscreening operations 609 a or 609 b. After the tank has filled it cansettle thereby clarifying the process water. The clarified process wateris pumped off the settled slurry and may be reused in the wet screeningoperation. The precious metals bearing slurry is now concentrated into amud/sludge fraction and bottom discharged and pumped out of settlingtank as bottom fraction 614.

Since the fraction 614 still contains some liquid, it is pumped into afilter press operation 615 from the settling tank. A filter press may befor example an air operated double diaphragm 1½-2″ pump and standardplate a frame filter press of appropriate size to handle the volume ofdesired filter cake. Full air is blown through the filter press toevacuate as much process water as possible. The filter press is thenopened, and each plate releases the precious metal bearing filter cake616 into a hopper for collection.

The filter cake 616 is then dried in operation 617 to remove allmoisture content, rendering a dry product suitable for shipment andacceptance to a precious metal smelter. A dryer may be for example a gasoperated sludge dryer manufactured by JWI or equivalent stainless-steelconveyor belt with attached feed hopper and standard heating zones. Thefeed hopper is loaded with a PGM bearing filter cake. The unit dropspellets of filter cake onto a stainless-steel conveyor and slowlyconveys material through gas fired heating zones. Dried material 106 bcontaining the PGMs exits the sludge dryer and is collected in a hopperprior to shipment to the precious metal smelter.

The equipment described above for the various operations in primary andsecondary recovery is illustrative; one or more embodiments may use anytypes of equipment to perform these operations. Equipment may beoff-the-shelf or custom built, or any combination thereof. For someoperations, equipment must meet certain specifications; for example, formechanical reduction of cryogenically cooled streams, equipment must bemade of materials that do not shatter when contacting the cooledstreams.

FIGS. 7 and 8 show an illustrative embodiment of customized equipmentthat may be used for example for cryogenic cooling step 501 of primaryseparation. This apparatus is an eight-vessel freezing carousel.Recyclable items are loaded into each vessel compartment on a conveyorsystem 701. Items are fed from the conveyor 701 into vessel 702 a. Eachouter freezing vessel is fabricated of stainless steel with hingedperforated stainless-steel inner baskets. Approximately 200 lb. of metalfoil catalytic converter substrates is loaded into each vesselcompartment. Liquid nitrogen is flooded into the vessel 702 a bydispenser 703 enough to cover the top layer. Vessel 702 a is thenrotated into discharge position 702 b, and the basket 702 c is tippedupward to discharge the frozen contents into jaw crusher 704, which liesbelow the carousel. Crushed material is discharged from the bottom 705of the jaw crusher 704. FIG. 8 shows a top view of the carousel, showingthe eight vessels, the loading and filling position 702 a, and thedischarge position 702 b. The carousel rotates in the sense 801, movingvessels from the loading position 702 a to the discharge position 702 b.The cycle time to rotate from loading to discharge positions issufficiently long to cool the material in the vessel to the target minus200 degrees to minus 250 degrees Fahrenheit.

While the invention herein disclosed has been described by means ofspecific embodiments and applications thereof, numerous modificationsand variations could be made thereto by those skilled in the art withoutdeparting from the scope of the invention set forth in the claims.

What is claimed is:
 1. A method of recovering materials bound to ametallic substrate using cryogenic cooling, comprising: obtaining asource stream comprising a multiplicity of recyclable items, eachrecyclable item comprising a metallic substrate; and one or more targetmaterials coupled to said metallic substrate, wherein said eachrecyclable item comprises all or a portion of a metal foil catalyticconverter substrate; said one or more target materials comprise one ormore of platinum, palladium, and rhodium; said each recyclable itemcomprises a fragment from said all or said portion of said metal foilcatalytic converter substrate that is generated by a primary recoveryprocess configured to recover a first portion of said one or more targetmaterials; and, said fragment comprises an additional quantity of saidone or more target materials that was not recovered in said primaryrecovery process; cryogenically cooling said source stream to form acooled stream, wherein a temperature of said cooled stream inducesembrittlement of said metallic substrate of said multiplicity ofrecyclable items; applying mechanical forces to said multiplicity ofrecyclable items in said cooled stream to break apart said metallicsubstrate into pieces, and to release all or a portion of said one ormore target materials from said metallic substrate, wherein saidapplying mechanical forces to said multiplicity of recyclable items insaid cooled stream comprises shattering fragments in said cooled streamusing an impact mill; forming a mixture stream comprising all or aportion of said pieces and said all or a portion of said one or moretarget materials; and, feeding said mixture stream into a separator toseparate said mixture stream into one or more first fractions containingsaid all or a portion of said pieces, and one or more second fractionscontaining said all or a portion of said one or more target materials.2. The method of claim 1, wherein one or more of said metallic substrateand said one or more target materials comprise iron or an iron alloy;and, said cryogenically cooling said source stream comprises mixing saidsource stream with liquid nitrogen to cool said cooled stream to atemperature at or below minus 150 degrees Fahrenheit.
 3. The method ofclaim 1, wherein one or more of said metallic substrate and said one ormore target materials comprise palladium or rhodium; and, saidcryogenically cooling said source stream comprises mixing said sourcestream with liquid nitrogen to cool said cooled stream to a temperatureat or below minus 200 degrees Fahrenheit.
 4. The method of claim 1,wherein one or more of said metallic substrate and said one or moretarget materials comprise platinum; and, said cryogenically cooling saidsource stream comprises mixing said source stream with liquid nitrogento cool said cooled stream to a temperature at or below minus 250degrees Fahrenheit.
 5. The method of claim 1, wherein said metallicsubstrate comprises a FeCrAl alloy; and, said cryogenically cooling saidsource stream comprises mixing said source stream with liquid nitrogenin a ratio of at least 1 liter of liquid nitrogen to each 1 kilogram ofFeCrAl alloy to cool said cooled stream to a temperature at or belowminus 200 degrees Fahrenheit.
 6. The method of claim 1, wherein saidseparator comprises a screen mesh.
 7. The method of claim 1, whereinsaid impact mill is constructed of one or more mill materials that donot shatter or break at said temperature of said cooled stream.
 8. Themethod of claim 7, wherein said one or more mill materials comprisestainless steel containing nickel.
 9. The method of claim 1, whereinsaid forming said mixture stream comprises screening said pieces andsaid all or a portion of said one or more target materials with anoutput screen, wherein a particles stream passes through said outputscreen; and, mixing said particles stream with a liquid to form saidmixture stream, wherein said liquid comprises an electrolyte and asurfactant.
 10. The method of claim 9, wherein said output screencomprises mesh size in a range of size 6 mesh to size 10 mesh.
 11. Themethod of claim 9, further comprising feeding said mixture stream intoan electrically grounded unit before said feeding said mixture streaminto said separator, wherein said electrically grounded unit isconfigured to agitate said mixture stream and to dissipate electricalcharge on particles in said mixture stream.
 12. The method of claim 9,wherein said separator comprises a screen mesh of mesh size in a rangeof 100 mesh to 150 mesh.
 13. The method of claim 9, further comprisingremoving moisture from said one or more second fractions.
 14. The methodof claim 13, wherein said removing moisture from said one or more secondfractions comprises feeding said one or more second fractions into asettling tank; waiting for said all or a portion of said one or moretarget materials to settle to a bottom of said settling tank; evacuatingliquid from a top of said settling tank to form a filter cake; and,drying said filter cake with heat.
 15. The method of claim 1, whereinsaid applying mechanical forces to said multiplicity of recyclable itemsin said cooled stream comprises crushing an outer can casing of saideach recyclable item to form crushed material; and, shredding saidcrushed material to form shredded material and to release said all or aportion of said one or more target materials from said crushed material;and, said mixture stream comprises said shredded material and said allor a portion of said one or more target materials.
 16. The method ofclaim 15, wherein said separator comprises a top screen comprising afirst mesh size, and a bottom screen comprising a second mesh sizegreater than said first mesh size; said one or more second fractionscontaining said all or a portion of said one or more target materialscomprise particles in said mixture stream that pass through said topscreen and said bottom screen; and, said one or more first fractionscontaining said all or a portion of said pieces comprise a large piecesfraction that does not pass through said top screen; and a small piecesfraction that passes through said top screen and does not pass throughsaid bottom screen.
 17. The method of claim 16, wherein said first meshsize is ¼ inches; and, said second mesh size is 10 mesh.
 18. The methodof claim 16, further comprising reintroducing said large pieces fractioninto said shredding; and, processing said small pieces fraction in asecondary recovery process to recover an additional quantity of said oneor more target materials that is bound to said small pieces fraction.19. A method of recovering materials bound to a metallic substrate usingcryogenic cooling, comprising: obtaining a primary source streamcomprising a multiplicity of recyclable items, each recyclable itemcomprising a metallic substrate; and one or more target materialscoupled to said metallic substrate; cryogenically cooling said primarysource stream to form a cooled primary stream, wherein a temperature ofsaid cooled primary stream induces embrittlement of said metallicsubstrate of said multiplicity of recyclable items; applying firstmechanical forces to said multiplicity of recyclable items in saidcooled primary stream to break apart said metallic substrate intopieces, and to release a first portion of said one or more targetmaterials from said metallic substrate; forming a first mixture streamcomprising all or a portion of said pieces and said first portion ofsaid one or more target materials; feeding said first mixture streaminto a first screen mesh separator to separate said first mixture streaminto a large pieces fraction comprising large pieces in said firstmixture stream that are larger than a first value; a small piecesfraction comprising small pieces in said first mixture stream that aresmaller than or equal to said first value and larger than a secondvalue; and a first target material recovery fraction comprisingparticles in said first mixture stream smaller than or equal to saidsecond value, wherein said first portion of said one or more targetmaterials is substantially in said first target material recoveryfraction; reintroducing said large pieces fraction into said applyingfirst mechanical forces; forming a secondary recovery source streamcomprising said small pieces fraction; cryogenically cooling saidsecondary recovery source stream to form a cooled secondary stream,wherein a temperature of said cooled secondary stream inducesembrittlement of said metallic substrate of said all or a portion ofsaid small pieces; shattering said small pieces in said cooled secondarystream using an impact mill, wherein said impact mill is constructed ofone or more mill materials that do not shatter or break at saidtemperature of said cooled secondary stream; screening an output of saidimpact mill with an output screen, wherein a particles stream passesthrough said output screen; mixing said particles stream with a liquidto form a second mixture stream, wherein said liquid comprises anelectrolyte and a surfactant; feeding said second mixture stream into anelectrically grounded unit, wherein said electrically grounded unit isconfigured to agitate said second mixture stream and to dissipateelectrical charge on particles in said second mixture stream; feedingsaid second mixture stream into a second screen mesh separator toseparate said mixture stream into a first final fraction containingmetallic residue, and a second final fraction containing a secondportion of said one or more target materials; feeding said second finalfraction into a settling tank; waiting for said second portion of saidone or more target materials to settle to a bottom of said settlingtank; evacuating liquid from a top of said settling tank to form afilter cake; and, drying said filter cake with heat.
 20. The method ofclaim 19, wherein said each recyclable item comprises all or a portionof a metal foil catalytic converter substrate; said one or more targetmaterials comprise one or more of platinum, palladium, and rhodium; saidmetallic substrate comprises a FeCrAl alloy; said cryogenically coolingsaid primary source stream comprises mixing said primary source streamwith liquid nitrogen in a ratio of at least 1 liter of liquid nitrogento each 1 kilogram of FeCrAl alloy to cool said cooled primary stream toa temperature at or below minus 200 degrees Fahrenheit; and, saidcryogenically cooling said secondary recovery source stream comprisesmixing said secondary recovery source stream with liquid nitrogen in aratio of at least 1 liter of liquid nitrogen to each 1 kilogram ofFeCrAl alloy to cool said cooled secondary stream to a temperature at orbelow minus 200 degrees Fahrenheit.
 21. A method of recovering materialsbound to a metallic substrate using cryogenic cooling, comprising:obtaining a source stream comprising a multiplicity of recyclable items,each recyclable item comprising a metallic substrate; and one or moretarget materials coupled to said metallic substrate, wherein said eachrecyclable item comprises all or a portion of a metal foil catalyticconverter substrate; and, said one or more target materials comprise oneor more of platinum, palladium, and rhodium; cryogenically cooling saidsource stream to form a cooled stream, wherein a temperature of saidcooled stream induces embrittlement of said metallic substrate of saidmultiplicity of recyclable items; applying mechanical forces to saidmultiplicity of recyclable items in said cooled stream to break apartsaid metallic substrate into pieces, and to release all or a portion ofsaid one or more target materials from said metallic substrate; forminga mixture stream comprising all or a portion of said pieces and said allor a portion of said one or more target materials; feeding said mixturestream into a separator to separate said mixture stream into one or morefirst fractions containing said all or a portion of said pieces, and oneor more second fractions containing said all or a portion of said one ormore target materials, wherein said applying mechanical forces to saidmultiplicity of recyclable items in said cooled stream comprisescrushing an outer can casing of said each recyclable item to formcrushed material; and, shredding said crushed material to form shreddedmaterial and to release said all or a portion of said one or more targetmaterials from said crushed material; said mixture stream comprises saidshredded material and said all or a portion of said one or more targetmaterials; said separator comprises a top screen comprising a first meshsize, and a bottom screen comprising a second mesh size greater thansaid first mesh size; said one or more second fractions containing saidall or a portion of said one or more target materials comprise particlesin said mixture stream that pass through said top screen and said bottomscreen; and, said one or more first fractions containing said all or aportion of said pieces comprise a large pieces fraction that does notpass through said top screen; and a small pieces fraction that passesthrough said top screen and does not pass through said bottom screen;reintroducing said large pieces fraction into said shredding; and,processing said small pieces fraction in a secondary recovery process torecover an additional quantity of said one or more target materials thatis bound to said small pieces fraction.